Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is a chronic, disabling illness that affects approximately 0.2% of the population.

Non-restorative sleep despite sufficient or extended total sleep time is one of the major clinical diagnostic criterion; however, the underlying cause of this symptom is unknown.

This review aims to provide a comprehensive overview of the literature examining sleep in CFS/ME and the issues surrounding the current research findings.

Polysomnographic and other objective measures of sleep have observed few differences in sleep parameters between CFS/ME patients and healthy controls, although some discrepancies do exist.

This lack of significant objective differences contrasts with the common subjective complaints of disturbed and unrefreshed sleep by CFS/ME patients.

The emergence of new, more sensitive techniques that examine the microstructure of sleep are showing promise for detecting differences in sleep between patients and healthy individuals.

There is preliminary evidence that alterations in sleep stage transitions and sleep instability, and other physiological mechanisms, such as heart rate variability and altered cortisol profiles, may be evident.

Future research investigating the etiology of non-restorative sleep in CFS/ME may also help us to uncover the causes of non-restorative sleep and fatigue in other medical conditions.